Such temporary filters are known, particularly by Patent FR-A-2 580 504. They are fixed to the distal end of a catheter for introduction and their structure is such that, during introduction into the vein, the elements ensuring filtration are folded into a sheath extending the catheter, and, when the filter has been placed in the vein, said filtering elements open out according to remotely controlled means. In the filter of FR-A-2 580 504, the filtering means are legs which extend, at rest, approximately parallel to one another along the generatrix of a cylinder and the means for opening them out are reversible expansion means located inside the cylinder defined by the filtering legs; by deformation, the expansion means exert on the legs a thrust from the inside so as to open them out in the manner of the spokes of an umbrella, by a sufficient amplitude for each leg to be applied at least in its distal zone against the wall of the vein.
These known filters present two drawbacks: On the one hand, they necessitate a complementary sheath for protecting the filtering legs, arranged at the distal end of the catheter, and adapted to be withdrawn when the filter is opened out in the vein. On the other hand, they require complementary, complex expansion means for opening out the filtering elements, remotely controllable in reversible manner, for example an inflatable balloon with a conduit supplying the corresponding fluid. This renders the structure of the filter and catheter assembly complex and delicate.
In order to overcome the drawbacks set forth hereinabove, document FR-A-2 606 642 proposes a filtering element which is borne at the distal end of the catheter and which comprises a plurality of flexible legs; the opposite ends of these flexible legs are interposed between two members joined together by a means for modifying the relative positions thereof, with the result that approach of the two members along the longitudinal axis provokes the transverse expansion of the flexible legs.
One embodiment cited in document FR-A-2 606 642 provides that the flexible legs result from the cut-out of the tube constituting the distal part of the catheter, said distal part being fast with an inner conduit which may slide longitudinally inside the tube.
This embodiment is particularly simple.
However, Applicant has observed that the presence of such a filter-catheter in a vein might cause blood clots to appear, localized in the immediate proximity of said filter.
It is an object of the present invention to propose a filter-catheter of the type mentioned above, which overcomes the drawback observed.